1. Field of Invention
This invention relates to beverage dispensing and in particular to a method and apparatus for controlling liquid flow, such as of syrup and of carbonated water.
2. Description of the Prior Art
Flow controls for postmix beverage dispensers are well-known. Two flow controls are commonly located in each dispensing valve of a beverage dispenser and are pressure compensated devices to control the syrup and soda flow rates through the valve to control, in turn, the ratio of syrup to water in the final beverage. These flow controls usually include piston-sleeve assemblies machined out of stainless steel or ceramic to very close tolerances. These known flow controls have certain disadvantages. They are expensive to machine; they leave an annular space between the piston and sleeve which allows leakage; they are subject to binding when a particle gets between the piston and sleeve; and a relatively large force is needed to move the piston if the large surface area between the piston and the sleeve becomes scratched.
Takahashi et al. (U.S. Pat. No. 4,648,424) disclose a liquid flow controller having a casing in which a valve body is slidably accommodated.
Erickson (U.S. Pat. No. 3,422,842) discloses an adjustable flow control device having a hollow piston slidably and loosely mounted within an associated casing and having a substantially friction free diaphragm for eliminating the by-passing of fluid about the exterior of the piston.
Heginbottom (U.S. Pat. Nos. 1,498,689 and 1,441,082) discloses a piston with resilient guide members which are connected to a disk-shaped portion of the piston head.